The invention relates to a device for writing information onto an information carrier.
From U.S. Pat. No. 5,126,985 a device is known for writing information onto an information carrier of the thermomagnetic type. The known device has a transducer for generating physically detectable patterns in the information carrier. The transducer includes an optical write head and a magnetic write head. The device includes a synchronizing circuit for deriving control signals for the optical and the magnetic write head from the information signal. The synchronizing circuit comprises a phase-locked loop which derives a clock signal from the information signal and a delay element which supplies a delayed clock signal as write signal. As higher information densities and higher writing speeds are required it is necessary to control the instants of occurrence and the lengths of variations in the write signal more precisely. The precision of these parameters can be improved to a certain extent by increasing the clock frequency with which the circuits are synchronized. However, the maximum permissible clock frequency is limited.
It is an object of the invention to further improve the precision of said parameters without the clock frequency having to be raised. To this end, the invention provides a device for writing information onto an information carrier, which device includes conversion means for converting symbols in an information signal into pulse sequences in a control signal and a transducer for generating a physically detectable pattern on the information carrier in response to the control signal, which conversion means include assignment means for assigning properties of the pulse sequences to symbols in the information signal, which properties include the duration and the magnitude of pulses in the pulse sequences, which conversion means further include at least one counter for supplying a count signal after expiry of a time interval, which counter is coupled to the assignment means, wherein the conversion means further include a controllable delay line coupled to the at least one counter, for delaying the count signal, and to the assignment means.
In the device in accordance with the invention the conversion means convert the symbols of the information to be written, for example EFM encoded information, into sequences of pulses having a duration and an amplitude. By means of the counter a comparatively coarse control of the duration of the pulses is obtained, which is limited by the maximum clock frequency with which the counter can be synchronized. However, the controllable delay line makes it possible to delay the counting signal with a time resolution which is far more accurate than that of the clock signal and thereby further increase the precision of said parameters of the pulses to be generated.